This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP00/07021 (not published in English) filed Oct. 10, 2000.
This invention relates to a swash plate refrigerant compressor, and more particularly to a swash plate refrigerant compressor suitable for use as a refrigerant compressor for an automotive vehicle, using CO2 (carbon dioxide) as a refrigerant.
FIG. 6 is a longitudinal cross-sectional view of a conventional swash plate refrigerant compressor, and FIG. 7 is an enlarged partial view of FIG. 6.
The swash plate refrigerant compressor includes a cylinder block 101 having a plurality of cylinder bores 106 formed therein, a shaft 105 rotatably supported in a central portion of the cylinder block 101, a swash plate 110 tiltably and slidably fitted on the shaft 105 and connected to a thrust flange 140 via a linkage 141, a crankcase 108 in which the swash plate 110 and the thrust flange 140 are received, and pistons 107 each of which is connected to the swash plate 110 via a shoe 150 which can perform relative rotation on a sliding surface 110a of the swash plate 110, the pistons 107 each reciprocating within a corresponding one of the cylinder bores 106 as the swash plate 110 rotates.
The inclination of the sliding surface 110a of the swash plate 110 with respect to an imaginary plane, not shown, orthogonal to the shaft 105 varies with pressure within the crankcase 108.
The shoe 150 is comprised of a dish-shaped shoe body 151 for relatively rollably supporting a forward end face of a ball 111a formed on one end of a connecting rod 111 and an annular washer 152 for relatively rollably supporting a rearward end face of the ball 111a. 
A retainer 153 for retaining the washer 152 of the shoe 150 is mounted on a boss 110b of the swash plate 110 via a radial bearing 155. The retainer 153 is relatively rotatable with respect to the swash plate 110. The radial bearing 155 is prevented from falling off by a stopper 154. The connecting rod 111 has another end 111b thereof secured to a corresponding one of the pistons 107.
As the shaft 105 rotates, the swash plate 110 also rotates in a state inclined with respect to the imaginary plane orthogonal to the shaft 105. The rotation of the swash plate 110 causes relative rotation of the shoe 150 on the sliding surface 110a of the swash plate 110 with respect to the swash plate 110, whereby rotation of the swash plate 110 is converted into linear reciprocating motion of the piston 107.
As a result, the volume of a compression chamber 122 within the cylinder bore 6 changes, whereby suction, compression, and delivery of refrigerant gas are sequentially carried out to deliver an amount of refrigerant gas corresponding to an inclination angle of the swash plate.
It should be noted that since the swash plate 110 is inclined with respect to the imaginary plane orthogonal to the shaft 105, when the swash plate 110 receives a compression reaction force from the refrigerant gas, tilt loads R1, R2 of the piston 107 are generated as shown in FIG. 7.
In the case of the swash plate refrigerant compressor using CO2 as the refrigerant, the difference (approximately 15 MPa at the maximum) between high pressure and low pressure is extremely large, so that a compression reaction force generated during compression of the refrigerant is larger than in a conventional swash plate refrigerant compressor using chlorofluorocarbon as the refrigerant. This results in increased tilt loads R1, R2 of the piston 107.
Further, in the case of the swash plate refrigerant compressor using CO2 as the refrigerant, lubricating oil separated by an oil separator, not shown, arranged in an intermediate portion of a path from a discharge chamber 112 to a discharge port 103a is returned into the crankcase 108, and attached to an outer peripheral surface of a bottom face-side end portion of the piston 107 when the piston 107 is close to its bottom dead center position, whereby the lubricating oil is supplied into a corresponding one of the cylinder bores 106. However, since a piston clearance (i.e. a gap between the outer peripheral surface of a piston and the inner peripheral surface of a cylinder bore) is not large, the amount of lubricating oil supplied to a top face-side end portion of the piston 107 is small.
Moreover, the lubricating oil circulates within the compressor without flowing out into a refrigerating cycle, so that refrigerant gas drawn into a compression chamber 122 contains very little lubricating oil, and hence only a small amount of lubricating oil is supplied to the top face-side end portion of the piston 107, which increases a sliding frictional force between the top face-side end portion of the piston 107 and the cylinder bore 106.
Therefore, the cylinder bore 106 is prone to abrasion (biased abrasion), and a coating film on the outer peripheral surface of the piston 107 is prone to peel-off.
It is an object of the invention to provide a swash plate refrigerant compressor which is capable of dividing and distributing tilt loads of pistons as well as enhancing lubricating oil-holding capability of the pistons.
To achieve the above object, the present invention provides a swash plate refrigerant compressor including a cylinder block having a plurality of cylinder bores formed therein, a drive shaft rotatably supported in a central portion of the cylinder block, pistons slidably inserted in the cylinder bores, respectively, a swash plate for transmitting a driving force to the pistons, and a crankcase in which the swash plate is received, and wherein an outer diameter of a top face-side end portion of the pistons is slightly smaller than an outer diameter of a hollow cylindrical portion of the pistons other than the top face-side end portion.
The outer diameter of the top face-side end portion of each piston is slightly smaller than that of the hollow cylindrical portion of the piston other than the top face-side end portion, as described above. Therefore, the tilt load of the top face-side end portion of the piston is divided and distributed onto two points, and at the same time, lubricating oil is held on the top face-side end portion of the piston. This ensures high lubricating oil-holding capability of the top face-side end portion of the piston, and hence it is possible to enhance slidability of the piston without increasing the clearance between the outer peripheral surface of the piston (hollow cylindrical portion) and the inner peripheral surface of the corresponding cylinder bore (i.e. without degrading volumetric efficiency). As a result, wear of the cylinder bore is reduced, and a coating film on the outer peripheral surface of the piston is made more peel-proof.
Preferably, inclination of the swash plate varies with pressure within the crankcase to thereby change a stroke length of the pistons.
As the inclination of the swash plate (with respect to an imaginary plane orthogonal to the drive shaft) increases, the tilt load of the piston also increases. However, since the outer diameter of the top face-side end portion of the piston is slightly smaller than that of the hollow cylindrical portion of the piston other than the top face-side end portion, the tilt load of the top face-side end portion of the piston is divided and distributed onto two points, and at the same time, lubricating oil is held on the top face-side end portion of the piston, thereby maintaining slidability of the piston.
Preferably, the top face-side end portion of the pistons is tapered.
The top face-side end portion of the each of the pistons is tapered, as described above, and hence the amount of lubricating oil held on the top face-side end portion of the piston is increased, which further enhances the slidability of the piston.
Preferably, inclination of the swash plate varies with pressure within the crankcase to thereby change a stroke length of the pistons, and the top face-side end portion of the piston is tapered.
Preferably, a lubricating oil groove is circumferentially formed in an outer peripheral surface of the top face-side end portion of the pistons.
The lubricating oil groove is circumferentially formed on the top face-side end portion of the each of the pistons, as described above, and hence, the amount of lubricating oil held on the top face-side end portion of the piston is increased, which further enhances the slidability of the piston.
Preferably, inclination of the swash plate varies with pressure within the crankcase to thereby change a stroke length of the pistons, and a lubricating oil groove is circumferentially formed in an outer peripheral surface of the top face-side end portion of the pistons.
Preferably, the top face-side end portion of the pistons is tapered, and a lubricating oil groove is circumferentially formed in an outer peripheral surface of the top face-side end portion of the pistons.
Preferably, inclination of the swash plate varies with pressure within the crankcase to thereby change a stroke length of the each of the pistons, and the top face-side end portion of the pistons is tapered, a lubricating oil groove being circumferentially formed in an outer peripheral surface of the top face-side end portion of the piston.
Preferably, carbon dioxide is used as a refrigerant.
When carbon dioxide is used as the refrigerant as described above, a compression reaction force generated during the compression is larger than in a conventional swash plate refrigerant compressor using chlorofluorocarbon as the refrigerant, and hence tilt load is also increased. However, the tilt load of the top face-side end portion of the piston is distributed, and at the same time, lubricating oil is held on the top face-side end portion of the piston, so that it is possible to enhance slidability of the piston without increasing the clearance between the outer peripheral surface of the piston (hollow cylindrical portion) and the inner peripheral surface of the corresponding cylinder bore. As a result, wear of the cylinder bore is reduced, and a coating film on the outer peripheral surface of the piston is made more peel-proof.